In typical commercial electrographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of development station commonly utilized in electrostatographic reproduction apparatus is the magnetic brush development station. The magnetic brush development station includes a housing containing a plurality of elements and providing a reservoir for a supply of developer material. The developer material may be, for example, a two-component material comprising magnetic carrier particles and relatively smaller pigmented marking particles. Included in the elements of the development station, a mixer assembly, such as a paddle wheel, auger, or ribbon blender, is located in the reservoir and serves to stir the carrier particles and marking particles to triboelectrically charge the particles so that the marking particles adhere to the surface of the carrier particles. A transport mechanism brings the developer material from the reservoir into the field of a plurality of magnets within a rotating sleeve, commonly referred to as the toning roller (of course, the magnets could rotate and the sleeve remain stationary or rotate with a different angular velocity from the magnets). The rotating sleeve and magnetic fields cause the marking particles to be brought into the vicinity of the latent image charge patterns on the dielectric support member to be applied to the latent image charge patterns in order to develop such patterns (see, for example, U.S. Pat. No. 4,887,132, issued Dec. 12,1989, in the names of Joseph et al).
It has been found that in manufacturing development stations of the above described type, it is difficult to obtain the desired distance (or gap) between the mixer assembly and the interior surface of the development station reservoir wall to get to the desired mixing performance. Further, it is difficult to keep the drive shaft for the mixer assembly and the drive shaft of the transport mechanism parallel to each other at final set-up. Both shafts are positioned and driven by a common gearbox. During initial set up, this gearbox is located relative to the development station housing by pins that substantially prevent horizontal or vertical movement therebetween. With the present achievable manufacturing variation and tolerances of the various elements and assemblies, the specified distance between the mixer assembly and the interior of the development station reservoir wall has not been readily obtainable or predictable. The mixer assembly and transport mechanism are positioned and secured to the development station housing by screws and are not held to a close position tolerance. Therefore, it has been impossible to keep the shafts of the mixer assembly and the transport mechanism parallel to each other.